The present invention relates to the field of radiographic imaging. In particular, the present invention provides a method and apparatus for generating accurate 3D models from 2D calibrated images. The method and apparatus of the present invention are useful in planning surgery and in sizing of orthopaedic implants, particularly when the joint or bone being supplemented or replaced has been damaged by injury or disease. The present invention may also be used in custom implant manufacture and fit.
In orthopaedic surgery the replacement of bone and joint parts is now in common use for disorders due to arthritis, prior injury, disease. Generally, at surgery, the part to be replaced is matched to the available parts in a given tool set using variously sized cutting blocks and trial implants. In many instances the trial parts do not fit the specific part accurately and the surgeon must decide to use a smaller or larger size.
As a means to solve this poor fit problem, CT and MRI imaging techniques have been used to generate specific, customized 3D models of the specific part to be replaced. From these models, using CAD/CAM techniques, a custom implant can be created. Cutting tools and blocks are needed to perfect the fit. But the use of CT and MRI imaging techniques are expensive, time consuming and not widely available.
One example of a specialized imaging system, that can generate an electronic model of a bone or joint is described by Sprouse et al. in US 2004/0199072, which describes a device that uses a coil array to generate a low energy magnetic filed around a patient. Sensors measure field strength at point in the field that are touched by a probe to build a 3D image of a bone or joint. The probe only touches the skin over-lying the bone or joint, so variations in soft-tissue depths, from patient to patient render this method somewhat inaccurate. Moreover, the physician using this method will not be provided with an actual image of the bone or joint in question, so anomalies in same cannot be assessed.
Bones and joints are irregular, biological vitally important structural elements of the mammalian skeleton.
The skeleton provides the structural support of vital organs (heart, liver, lungs) and the rigid entities (long bones) linked to mobile entities (joints) on which muscles, tendons and ligaments are set to provide motion.
Disease affects the musculoskeletal system in forms of joint disease, (arthritis) and bone deformity (fractures, infections, growth disorders). For correction of these maladies the medical and veterinarian community use images made using radiographs (most commonly radiographs such as X-Rays). The views made are uni-planar images which profile the skeletal structures relative to the muscular ones based on the high mineral content in the skeleton (osseous components of the bones and joints).
The difficulty in the interpretation of the images of the diseased M/S entities is the inherent variation and irregularities of the structures based on individual differences, which in turn are modified by disease. Thus in the human knee joint there are subtle differences in size (males larger than females) and shape (Asian versus western) yet shared general geometric and functional characteristics. Disease such as arthritis damages the joint's surfaces and modifies the shape and its structural/functional integrity. Examples are the common bow legged deformity and medial (inner) joint space collapse seen in Osteoarthritis affecting the medial compartment of the knee.